1. Field of The Invention
The present invention relates to the field of in vivo medication carriers for intravenous drug administration and methods of production. More particularly the present invention relates to the field of carrying of drugs in particulate vehicles which are porous and membraneless for intravenous drug administration and methods of production.
2. Description of The Prior Art
Conventional methods of drug administration include oral, intramuscular, subcutaneous, intraperitoneal, and intravenous injections. Of these methods, the intravenous approach allows the most direct and fastest equilibration with the blood stream which carries the medication to the rest of the body. However, peak serum levels are achieved within a short time of intravascular injection of any drugs. Toxic effects can result from such high serum levels, especially if the drug is given as a bolus injection. To avoid such high concentrations, drugs can be given slowly as a continuous drip. However, the latter method would require prolonged nursing care and possibly even hospitalization with its associated cost. Administration of drugs carried within stable carriers would allow bolus intravenous injections but gradual release of the drugs inside the intravascular compartment.
Another consideration of drug release is the uptake of the carrier by the reticulo-endothelial system (RES), allowing greater delivery of drugs to the liver and spleen. Alternatively, if the carriers are small enough so that the phagocytic cells (e.g. macrophage) do not preferentially ingest them, the carriers would escape the RES long enough to perform other tasks. One such interesting and medically useful task would be targeting of drugs to a specific population of cells. The targeting of specific cell types would be carried out by carriers which had antibodies or other ligands on the surface of the carriers directed against antigenic sites or specific receptors of these cells. Higher concentrations of drugs near the surface of the targeted cells and lower systemic side-effects would be desirable benefits from this approach.
Entrapment of biological agents are useful in other medical applications. For example, tiny air bubbles can create a strong contrast of the blood vessels (and the organs within which the blood vessels traverse) against the background during ultrasonography. However, the tiny air bubbles, if injected via a peripheral vein, must travel through the right heart, the pulmonary vasculature and then the left heart before they can reach to the other internal organs. Tiny air bubbles are inherently unstable and so they will not be able to stay in the required physical condition for effective ultrasonographic contrast by the time the intended organs are reached. Entrapment of the small air bubbles in small carriers will allow the air bubbles to serve their intended function even after long distances of travel within the intravascular compartment.
Similar advantages can be conferred to contrast material for CAT scans and nuclear magnetic resonance (NMR) scans. By entrapment of the contrast material during injection, the injection site will not have an abnormally high concentration of the contrast material leading to false interpretation of the results. However, the reticula-endothelial system (RES), such as the liver and the spleen, with the many phagocytic cells there, tend to phagocytize particulate matter. Uptake of contrast material such as paramagnetic metal ion chelate (e.g. Fe.sub.3 O.sub.4 and Gadolinium-DTPA chelate) by the RES would lead to digestion of carrier whereby the contrast agent is released for enhancement of the organs during magnetic resonance imaging.
Oxygen is another vital biological molecule that can be carried within the carrier if the carrier contains hemoglobin. It is now recognized that hemoglobin molecules, when given in large amounts, are toxic to the human body. Entrapment of hemoglobin within the carrier may reduce its toxicity to vital organs while allowing oxygen to be delivered.
From the above discussion it is clear that stable porous and membraneless carriers which allow rapid diffusion of biological molecules between their interiors and their environments offer many advantages. The two major approaches of microsphere synthesis in the prior art are liposomes and microspheres.
In liposomes, a shell is formed by a lipid layer or multiple lipid layers surrounding a central hydrophilic solution containing the medication. The lipid layers are inherently unstable and much research went into stabilizing them during the manufacturing process. In addition, the lipid layer(s) may serve as a barrier to diffusion of certain molecules. It is difficult for hydrophilic substrate to diffuse through the hydrophobic layers into the interior of the liposomes, or conversely, for the drugs to get out without physical destruction of the lipid layer(s).
Microspheres, in contrast to liposomes, do not have a surface membrane or a special outer layer to maintain its intactness. Most microspheres are more or less homogenous in structure. To maintain the stability of the microspheres, the manufacturing process in prior arts always includes a cross-linking process to stabilize the microspheric mass. However, the use of cross-linking agent in the manufacturing process will alter the chemical nature of the natural biological molecule, which may render the resultant product antigenic to the injected host. Anaphylactic reaction to such newly created antigenicity is unpredictable and dangerous.
The following prior art reference are found to be relevant to the field of the present invention.
U.S. Pat. No. 4,107,288 issued to Oppenheim et al. on Aug. 15, 1978 for "Injectable Compositions, Nanoparticles Useful Therein, And Process of Manufacturing Same" (hereafter "Oppenheim") discloses a process of making microspheres of cross-linked macromolecules by using cross-linking agents such as an aldehyde hardening agent (e.g. glutaraldehyde). In addition to the hardship in controlling the sizes of the microspheres formed, the Oppenheim process also produces many aggregations which are very undesirable for the purpose of an in vivo medication carrier.
U.S. Pat. No. 4,269,821 issued to Krauter et al. on May 26, 1981 for "Biological Material" (hereafter "Krauter") discloses processes for preparation of submicroscopic particles of physiologically acceptable polymer associated with a biologically active material by using a cross-linking agent such as a polymerisable material soluble in a liquid medium (e.g. methyl methacrylate).
U.S. Pat. No. 3,663,685 issued to Evans et al. on May 16, 1972 for "Biodegradable Radioactive Particles" (hereafter "Evans") discloses a method of preparing biodegradable radioactive particles by using heated wateroil solutions.
The article entitled "Magnetically Responsive Microspheres And Other Carriers For The Biophysical Targeting Of Antitumor Agents" written by Widder et al. and published in 1979 at ADVANCES IN PHARMACOLOGY AND CHEMOTHERAPY, Vol. 16, pp. 213-271 (hereafter "Widder") discloses emulsion polymerization methods of preparation of albumin microspheres (pp. 233-235) and preparation of magnetically responsive albumin microsphere (pp. 241-250). The methods essentially involve the processes of emulsification and heat denaturation of a water-oil solution to produce and stabilize microspheres. Widder has also mentioned that for heat sensitive drugs the microspheres are stabilized by chemical cross-linking.
As discussed above, some typical prior art processes, such as those used by Oppenheim et al. and Krauter et al., require the irradiation or heat or the presence and chemical reaction of a cross-linking agent to polymerize the "monomers" (which are the individual protein molecules such as human serum albumin or gelatin molecules) so that the resultant "polymers" will increase in molecular weight. When the mass has reached to the point that the solution cannot hold it in its soluble form, the mass will precipitate as a solid more-or-less spherical form which is the microsphere. The covalent bonding of the "monomers" into a "polymer" by the cross-linking agent provides the stability of the microsphere.
Other prior art methods, such as used by Widder et al. and Evans et al., use heat to cross-link and to stabilize the protein mass. Essentially, the emulsion consisting of microscopic protein droplets are heated in oil so that the proteins are denatured as a microscopic particle and stayed that way upon cooling and removal of the oily compounds. These protein molecules have been irreversibly denatured and rendered "foreign" to the host body.
U.S. Pat. No. 5,049,322 issued to Devissaguet et al. on Sep. 17, 1991 (hereafter "Devissaguet") discloses a method of producing a colloidal system containing 150-450 nm particles by dissolving a protein ingredient in a solvent and adding ethanol or mixture of ethanol containing surfactant. Devissaguet does not disclose adding a second protein ingredient. Devissaguet discloses a process of producing colloidal spheres which have a distinct "Wall" (column 2, line 25) or "layer" (column 8, line 33) of substance A which is different from the "core" of substance B (column 8, line 18), where the substance B may be a biologically active substance.
Devissaguet's method requires that substance A (the wall material) and substance B (the core material that is desired to be encapsulated) to be both present in the first liquid phase, which is then added to a second liquid phase that is a non-solvent for both substances A and B. Devissaguet's product consists of a "wall" formed by substance A, enclosing a "core" formed by substance B. It is clear the substance A is located physically in a different region than substance B, where substance A is on the outside and substance B is on the inside.
Albert L. Lehninger, Biochemistry: The Molecular Basis of Cell Structure and Function (1972) (hereafter "Lehninger") discloses that ethanol as a solvent can decrease the ionization of proteins and therefore promotes their coalescence and produces "colloidal suspensions". Lehninger does not disclose a special method of preparing colloidal suspensions, but rather generally a method of promoting protein coalescence by using ethanol, "[s]ince a decrease in dielectric constant increases the attractive force between two opposite charges, ethanol decreases the ionization of proteins and thus promotes their coalescence" (page 134, lines 21 through 25, citations omitted). Lehninger has defined the process of "coalescence" as a process leading to "insoluble aggregates" (page 133, lines 31 through 35). The desirable process, however, should not result in aggregates.
"Remington's Pharmaceutical Sciences", 7th ed. (1985) (hereafter "Remington") discloses some general knowledge of "colloidal dispersions". Remington teaches that adding surfactant "stabilizes the dispersion against coagulation" (page 286, column 2, lines 59 and 60), where the surfactant "arrange themselves at the interface between water and an organic solid or liquid of low polarity in such a way that the hydrocarbon chain is in contact with the surface of the solid particle or sticks inside the oil droplet while the polar bead group is oriented towards the water phase" (page 286, column 2, lines 30 through 35). Remington does not specially disclose the use of any particular protein molecules such as globin as the primary protein.
It is highly desirable to have an efficient synthetic method which does not involve the using of cross-linking agents nor heating, to thereby produce an effective carrier product which has desirable properties, including: (a) well controlled sizes, whether the goal is to produce carriers as small as 0.1 micron or as large as 7 micron in diameter; (b) stability against dilution (or removal of unreacted material by repeated washing) in a medium different from the one from which the carrier is synthesized; (c) stability against aggregation in various in vitro buffers with high or low osmolarity and in vivo.
The present invention is called "nanomatrixes" because some of them can be less than 50 nanomatrixes in diameter, although some can be as large as 4 to 5 microns. They are called "matrixes" because they do not have an enclosing membrane, much as a cotton ball having no need of a wrapper to maintain its shape. Their surfaces and interiors are continuously porous, which allows ready diffusion of molecules inward or outward.